Tungsten product and its manufacture



Patented Mar. 6', 1928.

UNITED STATES rarest tries.

ANTONIUS DE GRAAFF, OF EINDHOVEN, NETHERLANDS, ASSIGN 'OR I GENERAL ELEC- TRIG COMPANY, A CORPQR-ATION OF NEW YORK.

ruNesrnN rnonuor AND ITS MANUEAGTURE.

No Drawing. Application filed April 24, 1924,Serial No. 708,819, and in the Netherlands May 17, 1928.

My invention relates to improvements in the process of manufacturing tungsten filaments and in the filaments themselves.

Helically wound drawn filaments such as are at present frequentlyused in gasfilled glowlamps, are exposed to very high temperatures, owing to which the filaments become deformed and sag.

In order to prevent the sagging phenomena various attempts have already been made to exert influence on the dimensions and the shape of the crystals of the wire.

The sagging phenomena have been found to be suppressed to a marked extent, ifgt he filament contains a quantity of one or inp'gfe chromiumoxygen or manganeseoxygen compounds.

Good results are obtained if the finished filament contains 0005 to 0.1% of a chromiumoxygen or manganeseoxygen compound.

In the known process of manufacturing tungsten filaments. tungsten powder is pressed into rods, the rods are treated and then the product treated is further worked up until the desired dimensions are reached.

In the case of a given quantity of an alkali salt of a chromiumoxygen or manganeseoxygep compound being present in the tungsten powder, part of the said salt volatilizes while the treating operation is carried out and it has been found that the quantity of the oxygen compound remaining in the prpduct treated depends on the fineness of theltungsten powder. If the powder is too coarse and the rod pressed consequently too porous, the whole of the additions volatilizes during the treating operation; it on the. contrary the powder is too finely divided, it is not possible for the salt added to volatilize sufliciently so that too much of it remains.

It is possible that owing to the high temperature to which.it is exposed the alkali salt originally added is decomposed and that in the final product the alkali salt is no longer present but instead of it some chromiumoxygen or manganeseoxygen compound; it is only essential that an alkali salt 50 of a chromiumoxygen or manganese-oxygen compound be added to the starting product.

According to the invention a small quantity of an alkali salt of a chromiumoxygen or manganeseoxygen compound is added to the starting product and tungsten powder of a chromiumoxygen or manganeseoxygen compound instead of one single alkali salt.

Good results are for example obtained with the bichromates, chromates, manganates or permanganates of the alkali metals or mixtures thereof. I

The starting product to which the alkali salt is added, may be for example tungsten powder which should then have the necessary fineness.

The fineness of the tungsten powder can be regulated by properly choosing the circumstances in reducing the tungsten oxide. Thus the reducing temperature has a direct influence on the fineness of the powder obtained. It can be ascertained by experiments how the circumstances during the reduction process should be chosen in order to obtain a powder of a definite fineness.

A better and easier mingling of the compound added with the tungsten powder is ensured by adding a water solution of the compound to pure tungsten acid serving for the treating of the tungsten powder.

According to the invention a solution of the alkali salt may be added to tungsten acid, the mixture may be dried and then reduced under such circumstances that the tungsten powder obtained is so finely divided that in the product treated, a quantity of a chromiumoxygen or manganeseoxygen compound of at least 0.005% and at the utmost 0.1% remains.

As a rule the percent-age of alkali salt which is initially added is materially higher than the percentage of the compound which remains in the product treated. It depends on the fineness of the tungsten powder also on the nature of the substance chosen. For any particular case, the necessary percentage of the primarilyadded compound may be ascertained by experiments.

In a special case potassium bichromate may for example be added to'tungsten powder being so finely divided that 5 grams of the powder requires 40 seconds to fully settle down in com. of a mixture of alcohol and ether (1:1). It 0.24% of potassium bichromate is added, the product treated is found to contain a residue of 0.0050.03%

teristics of the tungsten that a non-sagging filament is obtained.

The following is an example of a process embodying the invention:

Impure tungsten acid is in the known manner dissolved in chemically pure ammonium hydroxide, filtered and crystallized.

and ammonium tungstate is thus obtained which by heat produces pure tungsten acid.

To this pure tungsten acid the required quantity for example 0.6% of potassium b1- chromate in solution is added. Whilst stirring continually the mixture is evaporated to dryness and the productobtained is then re-..

duced in a current of hydrogen. This is carried out under special circumstances for example at a temperature of about 800 so that the tungsten powder produced by the reduction is so finely divided that 5 grams thereof settle down in seconds in com. of a mixture of alcohol and ether in equal parts. I

The powder is further worked up in the known manner. It is pressed into rods, then it is fired and treated whereby a considerable part of the potassium bichromate volatilizes. The rod treated is then further mechanically worked up for example by hammering and rolling and lastly it is drawn into the diameter desired. The wire obtained may still be coiled, whereupon it is ready for use as a filament.

It will be seen, therefore, that my invention contemplates a finished metal or filam'ent for incandescent lamps which contains a small per cent of a sag preventing constituout, the object of the constituent being to reduce or eliminate the tendency of the finished metal or filament to sag during operation.

It is to be understood that modifications resulting from changes and substitutions and variations which will readily suggest themselves to those familiar with the art in view of the disclosure will fall within the contemplation of my invention and within the scope of the claims herein.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. The process of preparing a metal product which consists in mixing with a tungsten oxide a salt not exceeding 0.6% of the oxide, the oxide being in the formof a powof substantially equal parts and reducing the oxide, said salt serving to reduce the tendency ofthe filament to sag.

2. The process of preparing a finished metal for incandescent lamp filaments which consists in mixing a salt with tungsten oxide, the salt not exceeding 0.6% of the oxide, the mixture having the form of a powder, the fineness being substantially such that. 5 grams thereof will settle down in substantially 40- seconds in substantially 50 cubic centimeters of a mixture of alcohol and ether in substantially equal parts, pressingthe powder into rods and firing until the salt is reduced to below 1%,said salt bein a chromium salt and serving to reduce .t e tendency of the filament to sag.

3. The process of reparing a finishedmetal for incandesc'ent lamp filaments which consists in mixing a salt with tungsten oxide, the salt not exceeding 0.6% of the oxide,

powder into rods andfiring until the salt is reduced to below 1%, said salt bein an alkali chromium salt and serving to re uce the tendency of the filament to sag.

4. A tungsten filament for an incandescent lamp consisting of tungsten with a small per cent of a compound of one of the acid elements located in the periodic table in the righthand half of the third horizontal column, the per cent of the compound being less than 0.1% of the tifngsten, said compound operating to modify the tungsten con;- stituent to minimize the tendency of the fila ment to sag.

5. A tungsten lamp consisting of tungsten with a small per cent of a compound of chromium, the per cent'of the compound being less than 0.1% of the tungsten, said compound operatfilamentfor an incandescent 7 

